Organic EL elements are formed on substrates made of glass, plastic (including films), silicon wafers, or the like. Generally, organic EL elements have a stacked structure comprising a lower electrode, an upper electrode, and an organic layer disposed between the lower electrodes and the upper electrodes. The organic layer have a light-emitting layer made of light-emitting materials, as necessary, hole transport layers and/or electron transport layers and the like. When voltage is applied between the upper electrode and the lower electrode of the organic EL element to flow electric current, carriers (electrons and holes) injected from both electrodes are recombined in the light-emitting layers, which leads to light emission from the light-emitting layers.
In such organic EL elements, forming banks directly on the lower electrodes allows to enhance patterning accuracy of organic layers (ink). On the other hand, the thicknesses of the organic layers may become small at boundary portions between the banks and the lower electrodes due to repelling of ink droplets at the side surfaces of the banks. To avoid this problem, for example, Patent Document 1 refers a structure in which an inorganic insulating layer such as silicon oxide covering the periphery of a lower electrode is inserted between the lower electrode and a bank. In this method, because the inorganic insulating layer is formed by covering a boundary portion between the bank and the lower electrode, a dielectric strength voltage at the boundary portion between the bank and the lower electrode can be enhanced, which enables to suppress electric leak.
Patent Document 1: JP 2005-203215 A.